Phenomenon of surface plasmon of metals has been widely used nowadays. Researchers find if a special metallic nanostructure is disposed on an interface between dielectric materials, it can generate an interaction between electromagnetic waves and the metallic nanostructure and result in many novel optical characteristic. The optical characteristic can be controlled via modifying the structure, size, relative position, periodical arrangement of the metallic nanostructures and types of the dielectric materials around the metallic nanostructures. Therefore, special nanostructures can be fabricated via controlling the parameters of the metallic nanostructures to generate desired surface plasmon resonances, which can be applied in many photoelectronic products, photoelectronic measurements and academic researches. In the current stage, the surface plasmon waves have been applied to many fields, such as Raman spectrom measurement, thin film thickness measurement, optics constant measurement, solar cells, optical sensors, and biological sensors.
Particularly, surface plasma can also be applied to increasing the light luminous efficiency of light emitting diode (LED). It was found that the surface plasma effect produced at the interface between the metallic nanostructure and the dielectric material can magnify the action of the electromagnetic field and generate near-field effect, thus enhancing the luminous efficiency of the nearby quantum dots or quantum wells and promoting the light luminous efficiency and brightness of solid-state LED.
Besides, light generated by recombination of electrons and holes in quantum wells is omnidirectional. Thus, only the light emitted towards a direction away from the substrate is applicable unless there is a light guiding mechanism, and the light emitted towards the direction needs to penetrate heterogeneous layers to reach the air. During penetration, optical reaction produced inside the heterogeneous layers will cause a portion of the emitted light to be constrained inside the heterogeneous layers and converted into another form of energy. As a result, the emitted light is decreased layer by layer. If a surface plasmon structure is disposed on the interface between the heterogeneous layer and the air, the energy lost in the optical reaction can be easily absorbed and coupled. The surface plasmon structure can convert the momentum loss into photons and radiate the photons. The above-mentioned phenomenon is the so-called Localized Surface Plasmon Resonance (LSPR).
A Taiwan patent No. I395348 discloses a “Semiconductor Light Emitting Element”, which is an LED element having high light-emitting efficiency by using the technique of surface Plasmon. It discloses a metallic surface and a plurality of through-holes which are formed on the metallic surface and have a specified shape. Those through-holes are arranged in specified positions to form a metallic surface grating, which can excite generation of the surface plasma waves for achieving better light emitting efficiency.
Moreover, A Taiwan patent No. I363440 discloses “Light Emitting Element, Light Emitting Diode and Method for Fabricating the Same”. Briefly, an LED structure of this patent includes a surface plasmon coupling unit to generate surface plasmon waves and increase the luminous efficiency of LED.
The abovementioned conventional methods for fabricating specific nanostructures to generate surface plasma waves normally use technologies such as vapor deposition, sputtering coating, photo masks, pattern development and etching to form a plurality of metallic nanostructure regions, and then perform annealing process to transform the metallic nanostructure regions into spherical structures by the effect of surface tension. Therefore, the abovementioned conventional methods are complicated and expensive.
Besides, surface plasmon may be categorized into Surface Plasmon Polaritons (SPP) and Localized Surface Plasmon (LSP). The SSP exists on the interface between a metallic material and a dielectric material, wherein the LSP exists in a metallic nanostructure by a resonance mode. So far, the conventional technology is unable to apply the SSP and the LSP techniques in an identical systematic structure. The conventional technology is either unable to provide a cheaper process to generate the SSP and the LSP simultaneously.
In the conventional technology, surface plasmon can only exist in an interface between a metallic material and a dielectric material, which considerably constrains the design of surface plasmon generation structures. Therefore, the conventional technology still has room to improve.